Cylindrical target and its production method

ABSTRACT

A cylindrical target is obtained by joining a backing tube made of metal as an inner cylinder and a target material as an outer cylinder via a buffer member  52  such as a carbon felt. The cylindrical target broadens the possibility of selecting the target material and the material for a backing tube for supporting this, simplifies manufacturing and enables recycling.

TECHNICAL FIELD

[0001] The present invention relates to the structure of a cylindricaltarget to be applied to a magnetron sputtering apparatus (particularly,a direct-current magnetron sputtering apparatus) to be employed forforming a thin film, and its production method.

BACKGROUND ART

[0002] The magnetron sputtering method is known as one of techniques toform a thin film on a substrate of e.g. glass or plastic. JP-A-5-501587discloses a sputtering system employing a rotating cylindrical target.This apparatus has a magnet inside the cylindrical target, andsputtering is carried out while the target is cooled from the inside andthe target is rotated. The cylindrical target has advantages of a highefficiency of utilization and a high film-forming speed as compared witha flattened (planar type) target.

[0003] With respect to a production method of a cylindrical target,JP-A-5-214525 discloses a method of building up by a plasma spray methoda target material as a film material to be sputtered, on the outersurface of a backing tube made of e.g. stainless steel or titanium.Further, there has also been known e.g. a method of disposing a targetmaterial formed to have a cylindrical shape, on the outercircumferential surface of a backing tube, and inserting a metal such asindium between both members to bond them, or a method of forming aone-piece body including the part of the backing tube by the targetmaterial.

[0004] However, in the case of the plasma spray method, there is adisadvantage that the target material or the backing tube material islimited by the compatibility (for example, the difference in heatexpansion) between a material available for spraying and a material ofbacking tube. The method of bonding with e.g. indium requires a surfacetreatment to the outer circumferential surface of the backing tube andthe inner circumferential surface of the target material. Further, aheating apparatus for melting and injecting the indium into the bondingportion, and a consideration to prevent the melted indium from leaking,are also required. Further, in a case where the target material is madeof ceramics, the heat expansion rate of the target material is generallysmaller than that of the backing tube made of metal or that of indium asa bonding material, whereby a problem that a gap is formed at thebonding portion due to a shrinkage difference at the time of coolingafter the bonding, occurs.

[0005] Further, the target will be replaced when the target material isworn by sputtering. In a case of a target manufactured by a spray methodor an indium bonding method, the separation of the backing tube from thetarget material is difficult and therefore, such a target is notsuitable for reuse (recycling) of the backing tube.

[0006] On the other hand, although it is possible to form a one-piecebody including the part of the backing tube by the target material, thestructure of such one-piece type target does not have enough reliabilitybecause ceramics or some kinds of metal material have an insufficientstrength, or a low durability to a mechanical impact. Further, there isa problem of manufacturing cost if the one-piece body is formed by anexpensive target material.

[0007] The present invention has been made under consideration of suchcircumstances, and it is an object of the present invention to provide acylindrical target which can broaden the possibility of selecting thetarget material and the backing tube material, which can simplify themanufacturing, and which can increase the capability of reuse(recycling), and to provide its manufacturing method.

DISCLOSURE OF THE INVENTION

[0008] In order to achieve the above object, the cylindrical target ofthe present invention is characterized in that a hollow cylindricaltarget material is disposed on the outer circumference of a cylindricalbacking tube, and said backing tube and said target material are joinedvia a buffer material present between said backing tube and said targetmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a diagram of a cylindrical magnetron sputtering systemto which the cylindrical target of the present invention is applied.

[0010]FIG. 2 is a perspective view of the cylindrical target accordingto an embodiment of the present invention.

[0011]FIG. 3 is a cross-sectional view along a line 3-3 in FIG. 2.

[0012]FIG. 4 is an exploded perspective view of the cylindrical targetat the time of manufacturing according to an embodiment of the presentinvention.

[0013]FIG. 5 is a table showing an example of initial physical values ofa carbon felt and a carbon sheet.

[0014]FIG. 6 is a cross-sectional view illustrating an embodiment ofjoining a plurality of target materials.

[0015]FIG. 7 is a cross-sectional view of a cylindrical target with heatresisting O-rings inserted thereto.

[0016]FIG. 8 is a cross-sectional view illustrating another embodimentof joining a plurality of target materials.

EXPLANATION OF NUMERIC SYMBOLS

[0017] 10 Sealed reaction chamber

[0018] 12 Substrate

[0019] 14 Cylindrical target

[0020] 16 Backing tube

[0021] 17 Taper jig

[0022] 18 Magnet unit

[0023] 20 Target material

[0024] 20A Step portion

[0025] 22 Target driving device

[0026] 24, 26, 28 Magnetic pole

[0027] 30 DC power supply

[0028] 32 Power line

[0029] 34 Sliding contact point

[0030] 36 Outlet tube

[0031] 38 Vacuum pump

[0032] 40 First gas supply tube

[0033] 44, 50 Nozzle

[0034] 46 Second gas supply tube

[0035] 52 Electroconductive felt (buffer member)

[0036] 53 Heat resisting O-ring

BEST MODE FOR CARRYING OUT THE INVENTION

[0037] According to the present invention, a buffer member is presentbetween a target material as the material to form a film, and a backingtube (target holder) supporting the target material, whereby the volumechange due to their heat expansion difference can be absorbed by thebuffer member. Therefore, the degree of freedom of the combination ofthe target material and the backing tube material, will expand and moreproper selection of the materials will be possible. Further, theoperation of separating a worn target material from the backing tube iseasy, and the reuse of the backing tube is possible.

[0038] As an embodiment of disposing a buffer member between the targetmaterial and the backing tube, it is preferred to compressively pack acompression-deformable sheet-shaped buffer member between the backingtube and the target material. Here, the sheet-shaped buffer member maybe previously formed to have a cylindrical shape for use.

[0039] There is an embodiment of employing an electroconductive felt oran electroconductive sheet as said buffer member. According to anembodiment of the present invention, a carbon felt is applied as saidelectroconductive felt. Such a carbon felt preferably has a density offrom 0.05 to 0.5 g/cm³ in the initial state before it is compressivelypacked (hereinafter referred to simply as initial state) from theviewpoint of buffering performance.

[0040] The carbon felt employed in the present invention is preferablyhas a thickness of from 0.5 to 10 mm in the initial state, and thecompression ratio is preferably from 10 to 80% when it is compressivelypacked. Further, the carbon felt preferably has a volume resistivity inthe direction of thickness of from 0.1 to 100 Ω·cm in the initial statefrom the viewpoint of electric conductivity.

[0041] In order to provide a method of producing a cylindrical targethaving the above construction, the production method of the cylindricaltarget according to the present invention, is characterized in that abuffer member disposed on the inner surface of a target material havinga hollow cylindrical shape, a backing tube is inserted thereinto, sothat by this inserting operation, said buffer member is positionedbetween the outer circumferential surface of said backing tube and theinner surface of said target material, whereby said target material isjoined to said backing tube to obtain a cylindrical target.

[0042] As an embodiment of the above production method, there is anembodiment wherein a compression-deformable sheet-shaped buffer memberis provided on the inner surface of said target material, and by theinserting operation of said backing tube, said buffer member iscompressed, whereby said buffer member is packed between the outercircumferential surface of said backing tube and the inner surface ofsaid target material.

[0043] Further, the above buffer member such as a carbon felt, will bein a state that particles are apt to generate, when it is compressivelypacked. Therefore, in order to prevent the particle generation duringthe sputtering, it is preferred to dispose a seal member such as a heatresisting O-ring at the inner surface portion of each end of the targetmaterial.

[0044] In the following, preferred embodiments of the cylindrical targetaccording to the present invention and its production method will bedescribed with reference to the drawings attached.

[0045] At first, the construction of a magnetron sputtering systememploying the cylindrical target to which the present invention isapplicable, will be described with reference to JP-A-5-501587. FIG. 1 isa diagram of a cylindrical magnetron sputtering system. Here, thecylindrical target as identified by a numeric symbol 14 in the drawing,is illustrated in a cross-sectional view so as to show the internalstructure. A sealed reaction chamber 10 in which plasma is generated anda substrate 12 as an object to form a film is disposed, is kept invacuum. The cylindrical target 14 of the present invention comprises abacking tube 16 and a target material 20 disposed on the outercircumference of the backing tube 16. A compression-deformablesheet-shaped buffer member (electroconductive felt 52 in thisembodiment) is compressively packed between the backing tube 16 and thetarget material 20, whereby the backing tube 16 and the target material20 are joined. Here, as illustrated FIG. 1, a magnet unit 18 isaccommodated in the backing tube 16. The backing tube 16 is cooled bypassing a cooling liquid such as water therethrough.

[0046] The backing tube 16 holding the target material 20, is supportedby a target driving device 22 so that it can be rotated around itslongitudinal axis. In FIG. 1, a flattened substrate 12 is heldhorizontally, and the longitudinal axis of the cylindrical target 14 isalso held horizontally. However, the relative disposition between thesubstrate 12 and the cylindrical target 14 is not limited thereto.

[0047] A magnet unit 18 includes three rows of magnetic poles 24, 26 and28 disposed parallelly along the axis of the backing tube 16. Themagnetic poles 24, 26 and 28 are disposed to have N pole, S pole and Npole respectively, and lines of magnetic force pass through the backingtube 16 and enter into the neighboring magnetic pole having the oppositepolarity. By this magnetic pole disposition, a magnetic tunnel is formedto increase the sputtering speed.

[0048] The cathode potential V required to generate sputtering, isprovided from a DC power supply 30 through a power line 32 and a slidingcontact point 34 to the backing tube 16. Further, in order to obtain alow pressure required for sputtering, the sealed reaction chamber 10 isprovided with an outlet tube 36, to be connected to a vacuum pump, notshown.

[0049] The sealed reaction chamber 10 is provided with a gas supplymeans to supply gas required for sputtering. A first gas supply tube 40is arranged from an inert gas source, not shown, to the sealed reactionchamber 10. A nozzle 44 connected to the first gas supply tube 40,distributes an inert gas (e.g. argon gas) to the upper region of thecylindrical target 14. The inert gas introduced in the sealed reactionchamber 10, is ionized to collide with the surface of the targetmaterial 20 under the influence of electrical field in the magneticfield region.

[0050] A second gas supply tube 46 is extended from a reactive gassource, not shown, to the inside of the sealed reaction chamber 10. Anozzle 50 connected to the second gas supply tube 46, distributes areactive gas (e.g. pure oxygen) to the vicinity of the substrate 12 overits width. Molecules of the reactive gas are combined with moleculessputtered from the target surface as a result of the ionic collision, tothereby form predetermined molecules to be deposited on the surface ofthe substrate 12.

[0051]FIG. 2 is a perspective view of the cylindrical target accordingto an embodiment of the present invention, FIG. 3 is a cross-sectionalview along a line 3-3 in FIG. 2, and FIG. 4 is an exploded perspectiveview at the time of manufacturing the target. As illustrated in thesedrawings, the cylindrical target 14 is constituted by joining thebacking tube 16 made of metal as an inner cylinder and the cylindricaltarget material 20 as an outer cylinder, by compressively packing anelectroconductive felt 52 as a buffer member therebetween. Here, anelectroconductive sheet can be employed instead of the electroconductivefelt 52. However, the following description will be made by exemplifyingfelt.

[0052] The target material 20 is a hollow cylindrical member made ofmetal or ceramics as a film forming material, and such one having alength of from 0.4 to 4 m, an outer diameter of from φ80 to 150 mm, aninner diameter of from φ60 to 130 mm and a thickness of from 5 to 10 mmis, for example, employed. Specifically, metals such as Sn, Al, Zn, Ti,Ag, Mo, Si—Zr and Si—Sn, and electroconductive ceramics such as ITO,SiC, Al-doped ZnO and Sn-doped ZnO are, for example, be mentioned.Particularly an electroconductive ceramics is preferred. As the backingtube 16 supporting the target material 20, such one having a length offrom 0.4 to 4 m, an outer diameter of from φ60 to 130 mm, an innerdiameter of from φ50 to 120 mm, and a thickness of from 2 to 5 mm is,for example, employed so as to correspond to the dimension of the targetmaterial 20. As a material for the backing tube 16, a metal such asstainless steel, copper, titanium or molybdenum, may be used. Theelectroconductive felt 52 is a felt type sheet member made of fibershaving an electrical conductivity, and for example, a carbon felt (orsheet) made of carbon fibers, is applicable.

[0053] As illustrated in FIG. 4, the electroconductive felt 52 isprovided (wound) on the inner surface of the target material 20, andthey are fit to the outside of the backing tube 16 by employing aspecial jig (not shown). By this operation, the electroconductive felt52 is compressed. Whereby the target material 20 and the backing tube 16are joined. Here, at the front end portion of the backing tube 16, ataper jig 17 is attached to make the insertion easier.

[0054]FIG. 5 shows an example of initial physical properties of a carbonfelt and a carbon sheet useful in the above embodiment. As theelectroconductive felt (or sheet) 52, such one having, as the initialproperties (properties in a state before it is compressively packed), athickness larger than the gap between the inner diameter of the targetmaterial 20 and the outer diameter of the backing tube 16 is used. Ifthe dimension of the gap between the target material 20 and the backingtube 16 has a large variation, the electroconductive material may bepacked in the entire gap by employing a carbon felt which has a highercushion property than a carbon sheet.

[0055] For example, by compressively packing a carbon felt having aninitial thickness of from 0.5 to 10 mm (preferably from 1 to 5 mm), in agap of from 0.1 to 8 mm (preferably from 0.5 to 2.5 mm), the backingtube 16 and the target material 20 are joined. If the initial thicknessis smaller than 0.5 mm, the cushion property is not sufficientlyexhibited at the time of compressing. On the contrary, if the initialthickness is larger than 10 mm, there will occur such a problem thatwhen it is used as the target, the temperature of the target material 20will abnormally rise to cause a problem such as destruction because theheat insulating property being a characteristic of felt is too large.Further, the outer diameter of the target material 20 becomes too largeto use it because of the limitation of a device space.

[0056] The compression ratio of the felt when it is compressivelypacked, is from 10 to 80% (preferably from 30 to 60%). If thecompression ratio is smaller than 10%, the packed density is so smallthat shortage of the joining strength will occur. On the contrary, ifthe compression ratio is larger than 80%, the fibers constituting thefelt will be cut off and shortage of the joining strength will occur, orthe packed density becomes so large that the joining operation willbecome difficult.

[0057] The carbon felt (or sheet) is used as cut from, for example, arolled felt (or sheet) having a width of 1 m and a length of 5 m, into apiece having a size adaptable to the inner area of the target material20. The target material 20 is formed to have a length slightly shorterthan the length of the backing tube 16. The target material 20 does notneed to be a one-piece body having a length larger than the length inthe direction of width of the substrate 12 described in FIG. 1, and itmay have a construction such that the target material 20 is divided tohave a proper length to facilitate manufacturing. Then, the plurality oftarget materials 20 are serially connected. For example, FIG. 6 shows anembodiment that on a backing tube 16 having a length of 3 m, 10 piecesof the target material 20 each having a length of 295 mm are joined.

[0058] According to the cylindrical target 14 constituted as describedabove, there is a large difference in the heat expansion rate betweenthe backing tube 16 made of metal and the target material 20 made ofceramics. However, by positioning the electroconductive felt 52therebetween, a dimensional change due to the difference in the heatexpansion can be absorbed by the electroconductive felt 52. Therefore,the degree of freedom of the combination with respect to the material ofthe backing tube 16 and the target material 20, will be broadened, andmore proper selection of material will become possible.

[0059] When the target material 20 is worn, the target material 20 isseparated from the backing tube 16, and replaced by a new targetmaterial 20. In the case of the cylindrical target 14 according to thisembodiment, the operation of separating a worn target material 20 iseasy, and reuse of the backing tube 16 is possible.

[0060] Further, in the case of a hollow cylindrical target material 20made of ceramics such as silicon carbide (SiC), the inner surface of thehollow target is difficult to grind, and the accuracy of the dimensionis not so good if it is in a state of so-called “burnt surface”.However, in the case of the cylindrical target 14 of this embodiment,the electroconductive felt 52 having a cushion property, iscompressively packed between the target material 20 and the backing tube16 to join them. Accordingly, a high accuracy is not required for theinner dimension of the target material 20. Therefore, e.g. secondarygrinding of the inner circumferential surface is not necessary and themanufacturing is easy.

EXAMPLE 1

[0061] Now, more specific embodiment of the present invention will bedescribed with reference to Examples.

[0062] A cylindrical target for forming a SiO₂ thin film in a DCmagnetron sputtering apparatus, was produced as follows.

[0063] As a target material 20, a hollow cylindrical SiC burnt bodyimpregnated with Si having an outer diameter of φ152 mm, an innerdiameter of φ138 mm and a length of 220 mm was prepared, and six piecesof this were connected to have a total length of 1320 mm. Here, theinner circumferential surface and the outer circumferential surface ofthe target material 20 were left to be a burnt surface, and both ends ofthe burnt body were cut to make the length to be 220 mm. The accuracy ofthe inner and outer diameters were about ±0.5 mm due to e.g. deformationat the time of producing the burnt body.

[0064] The backing tube 16 for supporting the target material 20 wasformed by employing a commercially available tube made of SUS 304(according to JIS G3459: 135A (outer diameter)×Sch40 (thickness)), andgrinding it to have an outer diameter of φ136 mm, an inner diameter ofφ127 mm and a length of 1377 mm.

[0065] The target material 20 as an outer cylinder and the backing tube16 as an inner cylinder were joined by compressively packing a carbonfelt (having an initial state density of 0.12 g/cm³, and an initialstate volume resistivity in the direction of thickness of 8 Ω·cm) havinga thickness (thickness in the initial state) of 2 mm in the spacingtherebetween. Since the spacing is 1 mm in average, the compressionratio of the carbon felt at this time becomes 50%.

[0066] The carbon felt was used as cut from a commercially availablerolled felt having a width of 1 m and a length of 5 m, into a piecehaving a size adaptable to the inner area of the target material 20,namely 430 mm×220 mm.

[0067] The step of joining was such that a cut carbon felt was provided(wound) on the inner surface of the target material 20, and they werefit on the outside of the backing tube 16 by employing a special jig,and by repeating this operation, six pieces of the target material 20were joined to obtain a target material having a total length of 1320mm.

[0068] The special jig to be employed for the joining step was a devicewhich can fix the outer circumferential surface of a target material 20having a carbon felt provided (wound) on the inner circumferentialsurface, and can set a backing tube 16 so that it becomes coaxial withthe target material 20, whereby the backing tube 16 can be inserted intothe target material 20 by a hydraulic pressure.

[0069] Here, the joining can be carried out smoothly by attaching ataper-shaped jig (a member identified by a numeric symbol 17 in FIG. 4.)to the front end of the backing tube 16. This taper jig 17 will beremoved after the joining.

[0070] The cylindrical target thus obtained was attached to a DCmagnetron sputtering apparatus to carry out sputtering. The backpressure was 1.3×10⁻³ Pa, and the sputtering pressure was 0.4 Pa at thistime. Further, a mixture gas comprising oxygen/argon=1/1 (volume ratio)was employed as the sputtering gas. During the sputtering, stabledischarging was confirmed. It was further confirmed that on a glasssubstrate (which corresponds to a substrate 12 in FIG. 1) a desired SiO₂thin film was formed.

[0071] Further, the target material 20 worn by sputtering, can easily beremoved from the backing tube 16 by using the above special jig forjoining, and accordingly, the backing tube 16 can be reused.

[0072] Next, another embodiment of the present invention will bedescribed.

[0073]FIG. 7 is a cross-sectional view of a cylindrical target accordingto another embodiment of the present invention. In FIG. 7, the memberssame as or similar to these in FIG. 3 are indicated by the same numericsymbols, and description of these members is omitted. As illustrated inFIG. 7, in order to ensure the prevention of particle generation fromthe electroconductive felt 52 as a buffer member, it is preferred tocarry out step-forming grinding to inner surface of both ends of thetarget material 20 and heat resisting O-rings 53 are disposed at stepportions 20A. The material of the heat resisting O-ring 53 may, forexample, be nitrile rubber, styrene butadiene rubber, ethylene propylenerubber, polyacryl rubber, silicon rubber or fluorine rubber.Particularly, silicon rubber or fluorine rubber each having a high heatresistance, is preferred. The inner diameter of the heat resistingO-ring is preferably slightly smaller than the outer diameter of thebacking tube 16, and the thickness is preferably from 2 to 5 mm.

[0074] A specific description in the case of using the above heatresisting O-ring 53, will be made below.

EXAMPLE 2

[0075] A cylindrical target for forming an SiO₂ thin film in a DCmagnetron sputtering apparatus, was produced as follows.

[0076] As a target material 20, a hollow cylindrical SiC burnt bodyimpregnated with Si having an outer diameter of φ152 mm, an innerdiameter of φ138 mm and a length of 220 mm, was prepared and six piecesof this were connected to have a total length of 1320 mm. The innercircumferential surface of the target material 20 was left to be a burntsurface, the outer peripheral surface was ground, and both ends of theburnt body was cut to have a length of 220 mm, and further, the innersurface of both ends of the burnt body was ground to form steps. Theaccuracy of the inner diameter was about ±0.5 mm due to e.g. deformationat the time of preparing the burnt body.

[0077] The backing tube 16 for supporting the target material 20, wasformed by employing a commercially available tube made of SUS304(according to JIS G3459: 135A (outer diameter)×Sch40 (thickness)) andgrinding it to have an outer diameter of φ136 mm, an inner diameter ofφ127 mm and a length of 1377 mm.

[0078] The target material 20 as an outer cylinder and the backing tube16 as an inner cylinder were joined by compressively packing a carbonfelt (having an initial state density of 0.12 g/cm³ and an initial statevolume resistivity in the direction of the thickness of 8 Ω·cm) having athickness (initial state thickness) of 2 mm in the spacing therebetween.Since the spacing is 1 mm in average, the compression ratio of thecarbon felt becomes 50% at this time.

[0079] The carbon felt was used as cut from a commercially availablerolled felt having a width of 1 m and a length of 5 m, into a piecehaving a size adaptable to the inner area of the target material 20.Considering the thickness of the heat resisting O-rings 53 disposed oninner surface of both ends of the target material 20, the carbon felthaving a size in the direction of the length slightly smaller than thelength (220 mm) of the target material 20, is employed.

[0080] In this Example 2, the heat resisting O-rings 53 made of asilicon rubber having a thickness of 3 mm and a inner diameter of φ129mm, are employed. In this case, the dimension of the step portions 20Aare made to be 5 mm which is slightly larger than the thickness of theheat resisting O-rings 53. Accordingly, as the carbon felt, one having asize of 430 mm×210 mm, is employed.

[0081] In the joining step, a cut carbon felt was provided (wound) onthe inner surface of the target material 20, and they were fit on theoutside of the backing tube 16 by employing a special jig in the samemanner as in Example 1. Then, heat resisting O-rings 53 were arranged onthe inner surface of both ends of the target material 20. Theseoperations were repeated for six pieces of target material 20 tocomplete the joining of the target materials having a total length of1320 mm.

[0082] The cylindrical target thus obtained, can be used for sputteringin the same manner as in Example 1, and has an advantage that particlegeneration can be prevented for long period of time by a sealing effectof the heat resisting O-rings 53.

INDUSTRIAL APPLICABILITY

[0083] As described above, according to the cylindrical target and itsproducing method of the present invention, the structure that a hollowcylindrical target material and a backing tube for supporting this, arejoined via a buffer member such as a carbon felt present therebetween,is provided. Therefore, there are few limitations with respect to thecombination of the target material and the backing tube material,whereby more proper material selection becomes possible. Further,according to the present invention, the joining operation of the targetmaterial to the backing tube, and the operation to separate a worntarget material from the backing tube, are easy, and reuse of thebacking tube is possible, whereby a large economical effect can beobtained by reducing the manufacturing cost.

[0084] Further, the cylindrical target according to the presentinvention has an effect that between the target material and the backingtube, a buffer member is filled without gap, and accordingly, no gapwill be generated at the joining portion. Further, the producing methodof the cylindrical target according to the present invention, is easy tocarry out and can achieve a reduced cost of the cylindrical target.

[0085] The entire disclosure of Japanese Patent Application No.2000-273572 filed on Sep. 8, 2000 including specification, claims,drawings and summary is incorporated herein by reference in itsentirety.

What is claimed is:
 1. A cylindrical target characterized in that ahollow cylindrical target material is disposed on the outercircumference of a cylindrical backing tube, and said backing tube andsaid target material are joined via a buffer member present between saidbacking tube and said target material.
 2. The cylindrical targetaccording to claim 1, wherein a compression-deformable sheet-shapedbuffer member is compressively packed between the backing tube and thetarget material.
 3. The cylindrical target according to claim 1, whereinan electroconductive felt or an electroconductive sheet is employed assaid buffer member.
 4. The cylindrical target according to claim 3,wherein a carbon felt is employed as said electroconductive felt.
 5. Thecylindrical target according to claim 4, wherein said carbon felt has athickness of from 0.5 to 10 mm in the initial state before it iscompressively packed between said backing tube and said target material,and the compression ratio is from 10 to 80% when it is compressivelypacked.
 6. The cylindrical target according to claim 1, wherein saidtarget material is a hollow cylindrical member made of ceramics.
 7. Thecylindrical target according to claim 1, wherein a plurality of targetmaterials are joined to a single backing tube.
 8. A method of producinga cylindrical target, characterized in that a buffer member disposed onthe inner surface of a target material having a hollow cylindricalshape, a backing tube is inserted thereinto, so that by this insertingoperation, said buffer member is positioned between the outercircumferential surface of said backing tube and the inner surface ofsaid target material, whereby said target material is joined to saidbacking tube to obtain a cylindrical target.
 9. The method of producinga cylindrical target according to claim 8, wherein acompression-deformable sheet-shaped buffer member is provided on theinner surface of said target material, and by the inserting operation ofsaid backing tube, said buffer member is compressed, whereby said buffermember is packed between the outer circumferential surface of saidbacking tube and the inner surface of said target material.